Many known digital data processing devices such as electronic calculators compute and display data in either fixed-point or floating-point notation, as shown in the examples below:
______________________________________ Fixed-Point Floating-Point ______________________________________ 364.05 3.6405 +2 -364.05 -3.6405 +2 .036405 3.6405 -2 .036405 -3.6405 -2 ______________________________________
An electronic calculator of this type is described in the literature (see, for example, Hewlett-Packard Company Journal, Volume 20, No. 1, September 1968).
Floating-point notation is often used instead of fixedpoint notation in processing and displaying numerical data because the number of bits or digit places required to display large numbers in floating-point notation may be substantially less than the number of bits or digit places required to display similar large numbers in fixed-point notation. However, floating-point notation is often inconvenient for users making engineering, scientific or other measurements. The reason for this inconvenience is that many of the units measured such as millivolts, megahertz and the like are commonly represented in engineering notation (i.e., in multiples of 1,000 requiring an exponent that is a multiple of three). Users of devices that display data in floating-point format, therefore, often are compelled to mentally or manually rescale the data.
A computing counter (see Hewlett-Packard Company Journal, Volume 20, No. 9, May 1969) has been developed that displays data in engineering notation with the exponent expressed in alphabetic form rather than in numeric form, such as f in place of -15, p in place of -12, n in place of -9, .mu. in place of -6, m in place of -3, k in place of +3, M in place of +6, G in place of +9, and T in place of +12. This device, however, is limited to displaying only those numeric quantities for which there exists a commonly accepted alphabetic exponent notation. This device is also limited in the range of data that it can display because the size of the exponent display area is limited, and would be unduly large if required to contain all of the alphabetic characters necessary to represent every exponent that is a multiple of three, for example, in the range -99 to +99.
In performing certain measurements using digital data processing devices such as calculators, oscilloscopes, counters and the like, it is undesirable to be burdened with the inconvenience of rescaling floating-point data and the probability of error that such rescaling affords. It is also undesirable to be limited to displaying only data for which there exists an alphabetic exponent notation, thereby not being able to display very large or very small quantities such as 10.sup.33 or 10.sup..sup.-33 for which there are no commonly accepted alphabetic exponent notations.